The present invention relates to laser apparatus, and more particularly, to laser apparatus comprising cadmium sulfide (CdS) quantum dots in a room temperature liquid solution.
Semiconductor nanocrystal quantum dots have attracted great attention due to their tunable electronic and optical properties arising from three-dimensional quantum confinement effects. This is discussed in publications by A. P. Alivisatos, Science 271, 933 (1996), D. J. Norris and M. G. Bawendi, Physical Review B 53, 16338 (1996), and A. L. Efros and M. Rosen, Annual Review of Materials Science 30, 475 (2000).
The advantages of using semiconductor quantum dots in the strong confinement regime as gain media in lasing devices (due to their predicted reduced lasing threshold and improved temperature stability) are the driving forces in the development of semiconductor quantum dots based lasers. This is discussed in publications by Y. Arakawa and H. Sakaki, Applied Physics Letters 40, 939 (1982), and M. Asada, Y. Miyamoto, and Y. Suematsu, IEEE Journal of Quantum Electronics 22, 1915 (1986).
A large amount of study has been devoted to optical gain and amplified spontaneous emission (ASE) in semiconductor nanocrystals. Some of these publications address amplified spontaneous emission in the visible range with wavelengths longer than 500 nm using CdSe (540-680 nm). See for example, V. I. Klimov, A. A. Mikhailovsky, S. Xu, A. Malko, J. A. Hollingsworth, C. A. Leatherdale, H. J. Eisler, and M. G. Bawendi, Science 290, 314 (2000), A. A. Mikhailovsky, A. V. Malko, J. A. Hollingsworth, M. G. Bawendi, and V. I. Klimov, Applied Physics Letters 80, 2380 (2002), S. Link and M. A. El-Sayed, Journal of Applied Physics 92, 6799 (2002), V. C. Sundar, H. J. Eisler, and M. G. Bawendi, Advanced Materials 14, 739 (2002), and Y. Chan, J. M. Caruge, P. T. Snee, and M. G. Bawendi, Applied Physics Letters 85, 2460 (2004).
Another publication addresses the near-infrared range using PbSe (1425-1625 nm). See R. D. Schaller, M. A. Petruska, and V. I. Klimov, Journal of Physical Chemistry B 107, 13765 (2003). Another publication addresses the near-infrared range using InAs (1570 nm). See G. Chen, R. Rapaport, D. T. Fuchs, L. Lucas, A. J. Lovinger, S. Vilan, A. Aharoni, and U. Banin, Applied Physics Letters 87, 251108 (2005).
Furthermore, the observations of optical gain and ASE in quantum dots were from self-assembled close-packed quantum dot films or quantum dots in solid matrices, and none were in solution. For high power lasers, liquids are advantageous for heat circulation and dissipation.
As a direct wide band gap semiconductor, CdS nanocrystal quantum dots are an excellent candidate for realizing optical gain and ASE in the blue spectral range. Optical gain in sol-gel derived CdS nanocrystal quantum dots embedded in glass matrices pumped by intense nanosecond laser pulses was observed at low temperature (below 170° K) by Butty et al. in 1995. See J. Butty, Y. Z. Hu, N. Peyghambarian, Y. H. Kao, and J. D. Mackenzie, Applied Physics Letters 67, 2672 (1995).
With advances in incorporating quantum dots into host matrices, Chan et al. recently observed lasing in the blue spectral region from core-shell CdS/ZnS nanocrystals stabilized in a sol-gel derived silica matrix pumped by 100 femtosecond (fs) laser pulses at 400 nm. See Y. Chan, J. S. Steckel, P. T. Snee, J. M. Caruge, J. M. Hodgkiss, D. G. Nocera, and M. G. Bawendi, Applied Physics Letters 86, 073102 (2005).
However, until now, optical gain dynamics and measurement of optical gain lifetime have not been reported for CdS quantum dots and certainly not for a solution of CdS quantum dots at room temperature.
It would be advantageous to have lasing apparatus comprising cadmium sulfide (CdS) quantum dots in a room temperature liquid solution.